This collaborative effort brings together unique leprosy patient populations, epidemiological, clinical and laboratory expertise, and Mycobacterium leprae specific antigens in order to investigate in a concerted manner the clinical significance and pathobiological import of selected antigens and antibodies in the course of human infection. The antigens which are the major focus of these studies are phenolic glycolipid-I (PG-I), with its unique 3,6-di-O-methyl-Beta-D-glucopyranosyl determinant, and synthetic neo- and pseudo-glycoconjugates based on the sugar epitope. The patient and contact populations being studied in Micronesia include a hyperendemic subpopulation and one undergoing a "virgin soil" epidemic. The populations for study in the United States include its two largest outpatient leprosy clinic and contact populations, Hawaii and the Northern California area. These studies will focus in particular on preclinical serology of household and community contacts of infectious cases in order to provide, prior to actual onset, precursor indicators of impending onset of overt symptoms. Antiglycolipid antibodies, primarily of the IgM class, will be assayed by well established ELISA protocols. Glycolipid will be assessed by a combination of newly developed chemical and immunological-based assays. The levels of both antigen and antibody will be determined during the long incubation period, during effective therapy of established disease, in relapsing disease, and in various reactional states which commonly complicate therapy. Clinical correlations of antigen and antibody levels will be determined in order to define important clinical and epidemiologic patterns.